Stage effects are used to enhance the overall audience enjoyment of musical and theatrical performances. For instance, lighting of stage surfaces, props, performers, and even the audience itself may be achieved via strategically positioned lighting fixtures each configured to produce a desired lighting effect. Spot lights, Fresnel lamps, parabolic aluminized reflectors or PAR cans, and ellipsoidal reflector lamps are common examples of such fixtures. The lighting fixtures may be suspended overhead from trusses and controlled by an operator using a lighting board or control console. Mirror balls, smoke machines, pyrotechnics, and video devices are other examples of stage effects devices of the type that require electrical power and integrated control functionality.
In order to improve energy efficiency and enhance color control, traditional incandescent lamps may be replaced by solid-state lighting fixtures utilizing single or multi-colored light-emitting diodes (LEDs). LED fixtures are able to achieve lighting effects comparable to incandescent lamps while consuming a fraction of the power. As a result, 500-1000 W incandescent lamps are being replaced with solid-state lamps in the 20-100 W range, while certain emerging solid-state lamps of 250 W or more producing higher-power lighting effects.
Modern solid-state lighting fixtures generally have built-in power supplies and 120 VAC-rated power. Because conventional systems rely on 15 and 20 amp rated circuits, the power supplies and associated electrical connectors, cables, and supply circuitry tend to be unnecessarily expensive and bulky relative to the much lower power levels needed by new solid state light sources. Additionally, the new lighting hardware is vulnerable to power line surges, and also may pull a high inrush current when power is initially applied. In many cases, circuit breakers and electrical wiring must be overbuilt by four or more times with respect to the actual running power of the lighting fixtures in order to handle the large inrush current, thus negating potential cost savings from the solid-state efficiency gains.
Stage effects are typically controlled using multi-channel addressing according to the DMX-512 protocol, or DMX for short. The DMX protocol, which is ubiquitous in the entertainment field, is also used in architectural and landscape lighting applications. As a specialized application of the RS-422 serial communication standard, DMX is also a “multi-drop”-capable protocol that allows a number of lamp fixtures or other loads to be daisy-chained in a single run of cable that is terminated at the cable's endpoint. As such, DMX is useful in controlling large arrays of stage effects such as color-changing and moving lights, moving lasers, mirror ball rotation, and non-lighting stage effects. Using DMX512-A, for instance, 512 separate individually-addressable channels are available for transmission of 256 level increments or other commands to achieve a range of desired lighting effects, e.g., via transmission of digital bit strings.
An extension of the DMX protocol referred to as Remote Device Management (RDM) allows for limited two-way communication with a controlled device, e.g., the lighting fixtures and other devices noted above. RDM allows the controller to identify the lamp manufacturer type, serial number, software version, and operating and fault conditions of the RDM-enabled DMX device. DMX is traditionally carried over shielded twisted pair cables with 5 pin (and sometimes 3 pin) XLR-type connectors, with some movement toward using 4 pair data cable and RJ45 connectors of the type used for Ethernet network connections. Such cables provide the advantage of carrying DMX signals over inexpensive cables with quickly and reliably terminated connectors. In such a configuration, the extra conductors are left unused.
The Power over Ethernet (POE) standard provides electrical power and data through 4-pair cables and RJ45 connectors in certain low-power applications. Designed for powering computer monitors, switches, and voice-over-internet protocol (VOIp) telephones, POE is also currently used in some commercial lighting and security systems in which the power requirement to the individual fixtures is relatively low, and where it is desirable to have bi-directional communication, e.g., to communicate with occupancy sensors, ambient light sensors, and/or Ethernet-linked devices. CAT5 or CAT6 Ethernet cable may be used as part of the POE standard. CAT5 uses four twisted pairs of a 24-gauge electrical conductor. By comparison, CAT6 uses four twisted pairs of 23-gauge electrical conductors, while some emerging Ethernet cable designs use 22-gauge conductors. The POE standard requires that two conductor pairs in parallel provide 30 W of power, or that four pairs in parallel provide 60 W, with a cable run limit of 1000 feet.
However, the power levels made possible by POE remain inadequate for higher power lighting fixtures and other devices of the type used for stage lighting and other effects of the types described generally above, as is the requirement in the Ethernet protocol for separate cables leading from the hub to each controlled device. For instance, power transmission occurring over CAT5 Ethernet cable is generally limited to the above-noted 30-60 W power range at 48 VDC. The POE standard also requires data transformers and electronics with a high current rating and high-speed data coupling in order to allow transmission of both data and power over all four of the conductor pairs. Also, RJ45-type connectors are designed for data and for limited current, and are easily damaged by arcing during connection and disconnection, especially with inrush exceeding the current rating of the connector. CAT5 and similar cables are also limited in their capacity to provide significant current over the long distances required by POE standards, i.e., 600-1000 feet. CAT5 current handling capacity may be adequate over shorter lengths (25-100 feet) typical of a stage lighting system.